Obesity in Osborne-Mendel and S 5B/Pl rats: effects of sucrose solutions, castration, and treatment with estradiol or insulin.

S 5B/Pl rats were tested for their susceptibility to develop obesity when 1) ovariectomized, 2) given injections of insulin, and 3) given a sucrose solution to drink instead of water. The results obtained in Osborne-Mendel rats susceptible to dietary obesity when fed a high-fat diet were compared to those obtained in the S 5B/Pl rats not susceptible to dietary obesity. When tested at the end of 10 wk, ovariectomized rats of both strains had gained 22% more weight than sham-operated controls. Replacement estradiol injections suppressed food intake in both strains with a concomitant loss in body weight. Osborne-Mendel rats tolerated at least 40 U of U-100 protamine zinc insulin/day and rapidly gained weight whereas S 5B/Pl rats given more than 2 U U-100 protamine zinc insulin/day died. Compared to female Osborne-Mendel rats drinking water, rats drinking a sucrose solution accumulated more body fat and had higher levels of serum immunoreactive insulin and lower levels of serum free fatty acids. The substitution of a sucrose solution for plain drinking water suppressed weight gain in S 5B/Pl rats.